Question:
The number of coins 1.5 cm in diameter and 0.2 cm thick to be melted to form a right circular cylinder of height 10 cm and diameter 4.5 cm is
(a) 540
(b) 450
(c) 380
(d) 472
Solution:
(b) 450
Number of coins $=\frac{\text { volume of cylinder to be formed }}{\text { volume of a coin }}$
$=\frac{\pi \times 2.25 \times 2.25 \times 10}{\pi \times 0.75 \times 0.75 \times 0.2}$
$=\frac{225 \times 225 \times 5}{75 \times 75}$
$=450$
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